EXPERIENTIAL PROJECTOR MODEL OF HALLUCINATIONS

   A term that was introduced in or shortly before 1975 by the American psychopharmacologists Ronald K. Siegel and Murray E. Jarvik to denote a hypothetical model for the mediation of hallucinations. The model takes into account (1) the spontaneous mediation of endogenous imagery, (2) the role of arousal in the suppression or release of that imagery, and (3) the role of arousal in the projection of that imagery either into the 'mind's eye' or the outside world. The experiential projector model proceeds from the notion that the human perceptual system may be characterized as an information-processing system capable of processing sensory input by means of transformation, reduction, elaboration, storage, retrieval, anduse.Itgoesontosuggestthat"whenthesen-sory input that would normally give rise to perceptions is absent, man is either thinking, imagining, dreaming, or hallucinating.These quasi-perceptions are forms of mental imagery that lie on a continuum of intensity of vividness, thought images being the least vivid and images ofhalluci-nations being the most vivid. The transition from one form of imagery to another along this continuum depends on the arousal state; when arousal is low, there is still a baseline amount of spontaneous firings by cortical cells in normal waking behavior. This activity is suppressed and inhibited from entering into conscious awareness whenever one is asleep or new information is being scanned and processed. However, some introspection or thinking can retrieve the results of these firings, and they are presented as baseline imagery data. The information is projected in the mind's eye... With low arousal, such experiential projections are weak thought images. When arousal is increased, however, retrieval of information by this system is more successfully obtained ... The information may now appear to be more vividly projected and may contain increasing amounts of complex imagination and fantasy imagery. When arousal is further increased, information may appear to be projected on a sensory field outside the body, especially if other sensory inputs are reduced." Due to the authors' affinity with drug-induced hallucinations, and the "slideframe format in which these may appear, their experiential projector model takes the notion ofprojection quite literally. In the authors' own words, "Hallucinations occur when imagery is projected outside the observer and is viewed as separate from the projector." Conceptually, the experiential projector model may be seen as a variant of the 19th-century " perceptual release model.

   References

   Siegel, R.K., Jarvik, M.E. (1975). Drug-induced hallucinations in animals and man.In: Hallucinations. Behavior, experience, and theory. Edited by Siegel, R.K., West, L.J. New York, NY: John Wiley & Sons.